Under the Hood: Mobile star finder keeps it simple

Though I can't distinguish Scorpius from Sagittarius, I do enjoy perusing a star-filled sky. To help folks like me, as well as those who know more about star gazing, Celestron has created the SkyScout. This handheld viewing device can be used to identify or locate more than 6,000 celestial objects.

Named among the "Best of Innovations" at the 2006 Consumer Electronics Show, the SkyScout shipped midyear and remains on my personal "most interesting" list for innovative use of low-cost components. While some products that go through the teardown process reveal design approaches that more or less deliver what's expected, the SkyScout was a surprise in implementation as well as simplicity.

When it was first announced, my first guess was that the SkyScout might work by using pattern recognition and database matching of observed star formations  a challenging design task, and in hindsight a foolish guess on my part. The device does indeed use a database of celestial objects, but the database just holds a map, showing what stars and formations lie where in the three-dimensional space of space itself. More on that in a minute.

Usable as a standalone device or as an attachment to a telescope, the SkyScout measures about 18 x 10 x 7 centimeters and consists of the product enclosures, electronics and a built-in sighting apparatus.

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The device has no magnifying power. Instead it lets the user view the night sky through a set of two windows that are aligned along the long axis of its rubberized case. To aim the SkyScout, the user centers the star or constellation in the targets located on the front and rear sight windows. The operator can then push a simple "identify" button. An included headset lets the user listen to a description of the sky targeted by the SkyScout.

Alternatively, users can elect to find a celestial body. After the user chooses a star or constellation of interest from the extensive set of database options and presses the "locate" button, the SkyScout guides the user to the selected star(s) by a series of LED lamps that ring the viewfinder. As the device is moved around, the LEDs begin to blink more slowly (as the image moves further away) or more quickly (as motion brings the target closer within the viewfinder).

As it turns out, this fascinating tool uses no image recognition at all. Rather, the SkyScout simply needs to sense "where, when and in which direction." In this way, the objects seen in the viewfinder can be identified from and matched to the previously mentioned location-only database.

Think of the database as a virtual planetarium. The electronics determine where the device is pointed within the full sphere of the planetarium.

The trick then is to render the location, time and direction information without breaking the bank.

The first two pieces of information come from the SkyScout's built-in GPS. A PG4200 from Freescale contains the GPS receiver (and an associated 256-kbyte Samsung SRAM memory) to receive coordinate information and a time stamp. GPS chip sets have become quite inexpensive, and by leveraging the processing power of the Samsung S3C2410 host CPU, the receiver-only circuitry of the Freescale part adds little to the total bill of materials.